In recent years, there has been a demand to reduce tire rolling resistance from the perspective of fuel efficiency when a vehicle is traveling. In addition, there has been a demand for enhancement in wet performance from the perspective of safety. A known method of achieving this is a method of compatibility for low rolling resistance and wet performance by adding silica to a rubber component constituting the tread portion of a tire.
However, silica has low affinity with rubber components, and the cohesiveness between silica components is high, so if silica is simply added to the rubber component, the silica is not dispersed, which leads to the problem that the effect of reducing the rolling resistance or the effect of improving the wet performance cannot be sufficiently achieved.
In this connection, International Patent Publication No. WO/2011/105362 discloses a rubber composition including a conjugated diene-based rubber containing an isoprene block. In International Patent Publication No. WO/2011/105362, it is stated that by using the above composition, the affinity between the silica and the rubber is good, and reduced heat build-up (low rolling resistance) and wet grip performance can be enhanced.
In addition, there is also a demand for low viscosity in the rubber composition for a tire tread at the storage stage. In other words, there is a demand for excellent processability.
Meanwhile, environmental issues and resource problems have led to a demand for even fuel efficiency in vehicles, which in turn has led to a demand for further enhancements in the low rolling resistance of tires. In addition, in step with enhancements in the required safety level, there has also been a demand for further enhancements in wet performance and wear resistance.
In this connection, when the present inventors studied the rubber compositions described in International Patent Publication No. WO/2011/105362, there were cases where processability and wear resistance were poor, and it became clear that their low rolling resistance, wet performance, and processability do not satisfy the currently required levels.